Disclosed herein is a surfactant-free emulsion polymerization process for producing amphiphilic block copolymers. Further disclosed is a toner process comprising: (a) providing at least one amphiphilic block copolymer, wherein the amphiphilic block copolymer is prepared by surfactant-free emulsion polymerization comprising: dissolving at least one hydrophilic monomer in water; adding at least one hydrophobic monomer; optionally, adding a feed initiator; optionally, heating; to produce a colloidal dispersion of amphiphilic block copolymer; optionally, cooling; and optionally, discharging the produced colloidal dispersion of amphiphilic block copolymer; (b) contacting one or more components selected from the group consisting of a latex polymer, a wax; and a colorant with the colloidal dispersion of amphiphilic block copolymer to form a blend; or contacting the discharged amphiphilic block copolymer with one or more latexes or dispersions selected from the group consisting of a latex polymer, a polymer dispersion, a wax dispersion, and a colorant dispersion, and forming a dispersion; (c) heating the blend or dispersion at a temperature below the glass transition temperature of the latex polymer to form aggregated toner particles; (d) adding a coalescing agent to the toner particles thereby coalescing the toner particles; and (e) optionally, recovering the toner particles.
Raw materials for emulsion aggregation toners include various colloidal dispersions. Methods to obtain stable and functional colloidal dispersions are desirable for emulsion aggregation processes. It is desirable to develop improved, up-to-date methods for stabilizing organic, inorganic, and hybrid particles employed in emulsion aggregation toner processes. Dispersion agents, including surfactants and amphiphilic block copolymers, have been used in these processes. When used as surfactants, amphiphilic block copolymers have certain advantages over conventional small molecular weight surfactants, such as low critical micelle concentrations (CMCs), higher stability, less foaming, among other advantages. Further, amphiphilic block copolymers have application prospects in the fields of colloidal dispersions, adhesives, compatibilizers, dispersing agents for pigments and inorganic particles including quantum dots, and other fields.
Block copolymers can be prepared by living polymerization methods such as anionic polymerization, group transfer polymerization (GTP), nitroxide-mediated free radical polymerization, atom transfer radical polymerization (ATRP), or reversible addition-fragmentation chain transfer (RAFT) polymerization.
Most of the living polymerization approaches, such as GTP polymerization, require special and costly raw materials including special initiating systems and high purity monomers. Some of them have to be carried out under extreme conditions such as low moisture or low temperature. Further, some of these methods are sensitive to the active hydrogen groups on the monomers such as the hydroxyl and carboxylic acid groups. These groups would have to be chemically protected during the polymerization and recovered in a subsequent step. In addition, some of the initiating systems bring undesirable color, odor, metal complexes, or potentially corrosive halides into the product. Extra steps would be required to remove them.
Currently, the majority of the synthetic procedures for preparing amphiphilic block copolymers are based on controlled radical polymerizations (CRPs), which require elaborate and time-consuming synthesis. In fact, the implementation of CRPs in industry still remains limited due to the inevitable difficulties and disadvantages.
U.S. Patent Application Publication 2010/0081769, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a process for producing a linear block copolymer, useful as a dispersant for pigment, wherein the block copolymer comprises acetoacetyl amine functional groups which serve as pigment anchoring groups. The acetoacetyl amine functional groups can be formed by reacting hydroxyl functional groups with an acetoacetate agent and then reacting the resulted acetoacetate functional groups with a primary amine. The linear block copolymer can be an AB, ABC, or ABA block copolymer. The linear block copolymer produced by the present invention can be useful in dispersing and stabilizing a wide range of pigments in solvent based systems, and are particularly useful in providing pigment dispersions that are used in coating compositions for automobiles and trucks, where they provide improved efficiency of pigment use, lower paint viscosity, and reduced emission of volatile organic solvent. See also U. S. Patent Application Publication 2011/0144263, which is hereby incorporated by reference herein in its entirety, which describes in the Abstract thereof a linear block copolymer, useful as a dispersant for pigment, wherein the block copolymer comprises acetoacetyl amine functional groups which serve as pigment anchoring groups.
Currently available stabilizing and dispersing agents are suitable for their intended purposes. However a need remains for improved stabilizing and dispersing agents. Further, a need remains for improved stabilizing and dispersing agents for emulsion aggregation toner processes. Further, a need remains for improved processes for preparing stabilizing and dispersing agents, in embodiments, improved processes for preparing amphiphilic block copolymers that are suitable for such purposes.
The appropriate components and process aspects of the each of the foregoing U. S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.